The present application claims the benefit of Japanese Patent Application No. JP 10-62130, filed Feb. 25, 1998.
1. Field of the Invention
The present invention relates to a human c-Ha-ras proto-oncogenes transgenic rat, and a method for screening carcinogens, promoters of carcinogenesis, and preventing and inhibitory agents of carcinogenesis by using the present gene-engineered rat.
2. Description of the Background Art
The activated type of c-Ha-ras oncogene is detected at a high frequency in various human cancer tissues. A mouse carrying human c-Ha-ras proto-oncogene transgene has already been created and known as rasH2 mouse by Katsuki et. al., who have examined the relation between carcinogenesis and the activation of the transgene as well as the endogenous mouse Ha-ras gene. Their studies of the usefulness of the mouse as an animal for short-term screening of carcinogens are under way. However, organs in which tumor develop are limited to the lung, the skin, the forestomach and tumor induction in many other important organs such as gastrointestinal tracts, urogenital organs and endocrine organs is not satisfactory. Therfore, the transgene rasH2 mouse could not be used as a tool for the analysis of carcinogenesis and detection of carcinogens inducing tumors in such organs. A new animal model to conquer such problem has been desired.
For studies of chemical carcinogenesis, rats rather than mice are more frequently used for various reasons. In the liver carcinogenesis models, a variety of enzyme-altered condition has been studied for their relevance to carcinoma development. For example, an immunohisto-chemically demonstrable enzyme marker, glutathione S-transferase placental form (GST-P) has been utilized for the idetification of liver preneoplastic focal lesions. In contrast, no equivalent markers for preneoplastic foci are available for mice. Furthermore, unlike mice, mammary cancers in rats can be rapidly induced by N-metyhl-N-nitrosourea (MNU) administration without involvement of viral etiology. So far, only limited number of transgenic rats have been reported for studying carcinogenesis. Rats containing an albumin-promoter-fused to the simian virus 40 T antigen gene have been used to investigate GST-P expression in preneoplastic foci in the liver induced by the transgene and another transgenic rat containing the GST-P promoter fused to the chloramphenicol acetyltransferase gene has been analyzed to study regulation of GST-P transcripts in rat liver carcinogenesis.
Analysis of bladder carcinogenesis by use of rat superficial bladder cancer model induced with N butyl-N-(4-hydroxybutyl)nitrosoamine (BBN) can be performed because of its recombinant to humans and therefore, such studies are possible by use of human c-Ha-ras proto-oncogene transgene rat.
As has been described above, the human c-Ha-ras proto-oncogene transgenic rat has many advantages for not only screening of carcinogens and screening of promoters but also preventive and inhibitory agents of carcinogenesis.
We have generated transgenic rats using same gene construct employed for generation of human c-Ha-ras proto-oncogene transgenic mice, which has no mutations in the protein coding regions and no ability to transform NIH3T3 cells. In order to determine their susceptibility to mammary carcinogenesis, human c-Ha-ras proto-oncogene transgenic rats (Hras128 rats) were treated with MNU. Multiple large mammary carcinomas developed all rats 8 weeks after the carcinogen application. Gene mutational analyses indicated that transgene mutation did not play a major role in the enhancement of the carcinogen susceptibility, in contrast to the observation in non-transgenic rats.
The present invention relates to a human c-Ha-ras proto-oncogene transgenic rat (the term xe2x80x9cHras102xe2x80x9d or xe2x80x9cHras128xe2x80x9d may be used herein). Additionally, the present invention relates to a method for screening a carcinogen, a promoter as well as preventive and inhibitory agents of carcinogenesis,